Imaging lens

ABSTRACT

It is to provide an imaging lens that can improve optical performance while reducing size and weight. 
     An imaging lens includes, in order from an object side to an image surface side, a diaphragm, a first lens  3  that is a meniscus lens having a positive power whose convex surface faces the object side, and a second lens  4  that is a lens having a negative power whose concave surface faces the object side, wherein conditions expressed by the following expressions are to be satisfied: 0.25&lt;r 1 /r 2 ≦0.45, 0.35≦r 1 /FL≦0.42, and 0.85≦f 1 /FL≦1 (where, r 1 : center radius curvature of the object side face of the first lens, r 2 : center radius curvature of the image surface side face of the first lens, FL: focal distance of the entire lens system, and f 1 : focal distance of the first lens).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an imaging lens. In particular, thepresent invention relates to an imaging lens of a two-lens structurethat is capable of reducing size and weight and enhancing opticalperformance. The imaging lens is used for an image-taking device thatforms an image of an object, such as scenery and human figures, on animage-taking surface of a solid image pickup element such as a CCD,CMOS, etc. The solid image pickup element is mounted on a portablecomputer, a television phone, a portable phone, and the like.

2. Description of the Related Art

Recently, there has been an increasing demand for cameras that utilize asolid image pickup element, such as a CCD, CMOS, or the like, which ismounted on a portable phone, a portable computer, and a televisionphone, for example. It is demanded that a camera such as this is smalland light because the camera is required to be mounted on a limitedinstallation space.

Further, in recent years, there has been an increasing demand for ahigh-optical-performance lens system capable of sufficiently utilizingresolution capabilities of a solid image pickup element having a highresolution exceeding one million pixels. Achieving a balance betweensize and weight reduction and improvement in optical performance isbecoming increasingly important.

From this perspective, a two-lens structure lens system that is smallerand lighter than a three-lens structure lens system and superior to asingle-lens structure lens system in optical performance isadvantageous. Lens systems, such as those described in PatentLiteratures 1 to 6, have been proposed as such two-lens structure lenssystems.

-   [Patent Literature 1] Japanese Patent Unexamined Publication No.    2004-252067 (Especially, see FIRST EXAMPLE)-   [Patent Literature 2] Japanese Patent Unexamined Publication No.    2004-177628 (Especially, see FOURTH EXAMPLE and FIFTH EXAMPLE)-   [Patent Literature 3] Japanese Patent Publication No. 4074203    (Especially, See First Example)-   [Patent Literature 4] Japanese Patent Publication No. 4071817-   [Patent Literature 5] Japanese Patent Publication No. 4064434-   [Patent Literature 6] Japanese Patent Unexamined Publication No.    2004-170460

DISCLOSURE OF THE INVENTION Problems to be Solved the Invention

However, the lens systems described in Patent Literature 1 to PatentLiterature 3 are all disadvantageous in that a second lens is a lenshaving positive power, and effective aberration correction throughcombination of powers of a first lens and the second lens is difficultto achieve.

In addition, the lens systems described in Patent Literature 4 to PatentLiterature 6 are disadvantageous in that balance between curvature of anobject side surface of the first lens and curvature of an image surfaceside surface of the first lens is poor, making it difficult to achieveboth size and weight reduction and maintenance of high opticalperformance.

The present invention has been achieved in light of the above-describedproblems. An object of the invention is to provide an imaging lenshaving improved optical performance while being reduced in size andweight.

SUMMARY OF THE INVENTION

In order to achieve the aforementioned object, an imaging lens accordingto a first aspect of the present invention is an imaging lens used forforming an image of an object on an image-taking surface of an imagesensor element including, in order from an object side to an imagesurface side: a diaphragm, a first lens that is a meniscus lens having apositive power whose convex surface faces the object side, and a secondlens that is a lens having a negative power whose concave surface facesthe object side, wherein conditions expressed by the followingexpressions (1) to (3) are to be satisfied:0.25<r ₁ /r ₂≦0.45  (1)0.35≦r ₁ /FL≦0.42  (2)0.85≦f ₁ /FL≦1  (3)where,

r₁: center radius curvature of the object side face of the first lens

r₂: center radius curvature of the image surface side face of the firstlens

FL: focal distance of the entire lens system

f₁: focal distance of the first lens.

In the invention, when the diaphragm is disposed closest to the objectside, positioning of the diaphragm in a same position in an optical axisdirection as a point on the optical axis (referred to, hereinafter, as asurface apex) of a surface (convex surface) of the first lens on theobject side cannot be avoided. In addition, the surface apex andsurrounding area of the surface of the first lens on the object sidepassing through the diaphragm and being positioned (projecting) closerto the object side than the diaphragm cannot be avoided. Even in thisinstance, because the diaphragm is physically positioned closer to theobject side than the overall first lens, the configuration does notdepart from the description in the scope of claims. To reduce the sizeof the optical system, the diaphragm is preferably positioned closer tothe image surface side than the surface apex of the surface of the firstlens on the object side.

In the invention according to the first aspect, the diaphragm isdisposed closest to the object side. The first lens is a positivemeniscus lens that is convex on the object side. The second lens is anegative lens whose concave surface faces the object side. In addition,the conditions expressed by the expressions (1) to (3) are satisfied.Therefore, telecentricity can be ensured, aberration can be effectivelycorrected, and optical performance can be improved while achieving sizeand weight reduction. Furthermore, productivity can be improved.Productivity, herein, means not only the productivity for mass-producingthe imaging lens (such as moldability and cost when the imaging lens ismass-produced by injection molding), but also easiness of processing,manufacture, etc. of equipment used for manufacturing the imaging lens(such as easiness of processing a mold used for injection molding) (thesame applies hereinafter).

An imaging lens according to a second aspect is the imaging lensaccording to the first aspect in which a condition expressed by afollowing expression (4) is further satisfied:0.6≦d ₂ /d ₂≦1.25  (4)where,

d₁: center thickness of the first lens

d₂: distance between the first lens and the second lens on the opticalaxis.

In the invention according to the second aspect, the expression (4) isfurther satisfied. Therefore, a means for effectively blockingunnecessary light can be appropriately employed while maintainingproductivity.

An imaging lens according to a third aspect is the imaging lensaccording to the first aspect in which a condition expressed by afollowing expression (5) is further satisfied:0.65≦d ₂ /d ₃≦1.1  (5)where,

d₂: distance between the first lens and the second lens on the opticalaxis

d₃: center thickness of the second lens.

In the invention according to the third aspect, the expression (5) isfurther satisfied. Therefore, a means for effectively blockingunnecessary light can be appropriately employed while maintainingproductivity.

An imaging lens according to a fourth aspect is the imaging lensaccording to the first aspect in which a condition expressed by afollowing expression (6) is further satisfied:0.1≦d ₁ /FL≦0.3  (6)where,

d₁: center thickness of the first lens.

In the invention according to the fourth aspect, the expression (6) isfurther satisfied. Therefore, excellent balance can be achieved betweensize and weight reduction and maintenance of productivity.

An imaging lens according to a fifth aspect is the imaging lensaccording to the first aspect in which a condition expressed by afollowing expression (7) is further satisfied:0.1≦d ₃ /FL≦0.3  (7)where,

d₃: center thickness of the second lens.

In the invention according to the fifth aspect, the expression (7) isfurther satisfied. Therefore, productivity can be maintained whilereducing size and weight.

An imaging lens according to a sixth aspect is the imaging lensaccording to the first aspect in which a condition expressed by afollowing expression (8) is further satisfied:0.9≦L/FL≦1.2  (8)where,

L: overall length of the lens system (distance from the surface closestto the object side to the image-taking surface on the optical axis:equivalent air length).

In the invention according to the sixth aspect, the expression (8) isfurther satisfied. Therefore, balance can be achieved between size andweight reduction and maintenance of productivity.

In the imaging lens of the present invention, optical performance can beimproved while achieving size and weight reduction.

EFFECTS OF THE INVENTION

With the imaging lens according to the present invention, opticalperformance can be improved while achieving size and weight reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for showing an embodiment of the imaginglens according to the present invention;

FIG. 2 is a schematic diagram for showing FIRST EXAMPLE of the imaginglens according to the present invention;

FIG. 3 shows graphs for describing the astigmatism and distortion of theimaging lens shown in FIG. 2;

FIG. 4 is a schematic diagram for showing SECOND EXAMPLE of the imaginglens according to the present invention;

FIG. 5 shows graphs for describing the astigmatism and distortion of theimaging lens shown in FIG. 4;

FIG. 6 is a schematic diagram for showing THIRD EXAMPLE of the imaginglens according to the present invention;

FIG. 7 shows graphs for describing the astigmatism and distortion of theimaging lens shown in FIG. 6;

FIG. 8 is a schematic diagram for showing FOURTH EXAMPLE of the imaginglens according to the present invention;

FIG. 9 shows graphs for describing the astigmatism and distortion of theimaging lens shown in FIG. 8;

FIG. 10 is a schematic diagram for showing FIFTH EXAMPLE of the imaginglens according to the present invention;

FIG. 11 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 10;

FIG. 12 is a schematic diagram for showing SIXTH EXAMPLE of the imaginglens according to the present invention;

FIG. 13 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 12;

FIG. 14 is a schematic diagram for showing SEVENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 15 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 14;

FIG. 16 is a schematic diagram for showing EIGHTH EXAMPLE of the imaginglens according to the present invention;

FIG. 17 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 16;

FIG. 18 is a schematic diagram for showing NINTH EXAMPLE of the imaginglens according to the present invention;

FIG. 19 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 18;

FIG. 20 is a schematic diagram for showing TENTH EXAMPLE of the imaginglens according to the present invention;

FIG. 21 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 20;

FIG. 22 is a schematic diagram for showing ELEVENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 23 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 22;

FIG. 24 is a schematic diagram for showing TWELFTH EXAMPLE of theimaging lens according to the present invention;

FIG. 25 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 24;

FIG. 26 is a schematic diagram for showing THIRTEENTH EXAMPLE of theimaging lens according to the present invention;

FIG. 27 shows graphs for describing the astigmatism and distortion ofthe imaging lens shown in FIG. 26;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the imaging lens of the present invention will bedescribed hereinafter with reference to FIG. 1.

As shown in FIG. 1, an imaging lens 1 according to the embodimentincludes, in order from an object side toward an image surface side, adiaphragm 2, a first lens 3 made of resin that is a meniscus lens havinga positive power whose convex surface faces the object side, and asecond lens 4 made of resin that is a lens having a negative power whoseconcave surface faces the object side.

Respective lens surfaces of the first lens 3 and the second lens 4 onthe object side are referred to as a first face. Respective lenssurfaces of the first lens 3 and the second lens 4 on the image surfaceside are referred to as a second face.

An image-taking surface 5 that is a light-receiving surface of an imagesensor element, such as a charge-coupled device (CCD) or a complementarymetal oxide semiconductor (CMOS), is disposed on the second face side ofthe second lens 4. An image of an object is formed on the image-takingsurface 5 by incident light from the object side that has been convergedby the first lens 3 and the second lens 4.

Various filters, such as a cover glass, an infrared (IR) cut filter, anda low-pass filter, may be disposed as required between the second faceof the second lens 4 and the image-taking surface 5. The IR cut filtermay be formed on any one lens surface, such as a second face 3 b of thefirst lens 3, or on a plurality of lens surfaces, among the lenssurfaces of the first lens 3 and the second lens 4.

In this way, according to the embodiment, high telecentricity can beensured as a result of the diaphragm 2 being positioned closest to theobject side and an exit pupil position being positioned away from theimage-taking surface 5. Therefore, an incidence angle of a light beamincident on a sensor of the image sensor element can be relaxed.

According to the embodiment, the second lens 4 is a lens having anegative power, while the first lens 3 is a positive meniscus lens thatis convex on the object side. Therefore, effective aberration correctioncan be achieved through combination of powers of the second lens 4 andthe first lens 3.

Moreover, according to the embodiment, conditions expressed by followingexpressions (1) to (3) are satisfied:0.25<r ₁ /r ₂≦0.45  (1)0.35≦r ₁ /FL≦0.42  (2)0.85≦f ₁ /FL≦1  (3)where, r₁ in the expression (1) and the expression (2) is a centerradius curvature of a first face 3 a of the first lens 3 (the sameapplies hereinafter). r₂ in the expression (1) is a center radiuscurvature of the second face 3 b of the first lens 3 (the same applieshereinafter). FL in the expression (2) and the expression (3) is a focaldistance of the entire lens system (the same applies hereinafter). f₁ inthe expression (3) is a focal distance of the first lens 3 (the sameapplies hereinafter).

Here, when the value of r₁/r₂ is the value (0.25) shown in theexpression (1) or less, aberration correction effect on the second face3 b of the first lens 3 weakens. Achieving desired optical performance,while ensuring size and weight reduction of the overall optical system,becomes difficult. On the other hand, when the value of r₁/r₂ is greaterthan the value (0.45) shown in the expression (1), the center radiuscurvatures of both the first face 3 a and the second face 3 b of thefirst lens 3 become too small. An injection-molding mold used tomanufacture the first lens 3 by injection molding becomes difficult tomanufacture. Size and weight reduction of the overall optical systembecomes difficult to ensure.

When the value of r₁/FL is less than the value (0.35) shown in theexpression (2), the center radius curvature of the first lens 3 becomestoo small. The first lens 3 becomes difficult to manufacture. On theother hand, when the value of r₁/FL is greater than the value (0.42)shown in the expression (2), the overall optical system becomes toolarge. Size and weight reduction becomes difficult.

When the value of f₁/FL is less than the value (0.85) shown in theexpression (3), the power of the first lens 3 becomes too large comparedto the power of the overall optical system. The desired opticalperformance becomes difficult to achieve. On the other hand, when thevalue of f₁/FL is greater than the value (1) shown in the expression(3), the power of the first lens 3 becomes too small compared to thepower of the overall optical system. Size and weight reduction of theoverall optical system becomes difficult to achieve.

Therefore, according to the embodiment, by the value of r₁/r₂ being setto satisfy the expression (1), the value of r₁/FL being set to satisfythe expression (2), and the value of f₁/FL being set to satisfy theexpression (3), telecentricity can be ensured, aberration can beeffectively corrected, and optical performance can be improved whileachieving size and weight reduction. Furthermore, productivity can beimproved.

The relationship between r₁ and r₂ is more preferably 0.29<r₁/r₂≦0.4.

The relationship between r₁ and FL is more preferably 0.35≦r₁/FL<0.4.

The relationship between f₁ and FL is more preferably 0.9≦f₁/FL≦1.

According to a more preferable embodiment, a condition expressed by afollowing expression (4) is further satisfied:0.6≦d ₂ /d ₁≦1.25  (4)where, d₁ in the expression (4) is a center thickness of the first lens3 (the same applies hereinafter). d₂ in the expression (4) is a distancebetween the first lens 3 and the second lens 4 on an optical axis 6 (thesame applies hereinafter).

Here, when the value of d₂/d₁ is less than the value (0.6) shown in theexpression (4), the distance between the first lens 3 and the secondlens 4 becomes too narrow. Inserting a blocking shield or the likebetween the first lens 3 and the second lens 4 to effectively blockunnecessary light becomes difficult. In addition, edge sections ofrespective optical surfaces of the first lens 3 and the second lens 4become too close to each other, thereby increasing generation ofunnecessary light. On the other hand, when the value of d₂/d₁ is greaterthan the value (1.25) shown in the expression (4), the center thicknessof the first lens 3 becomes too thin. Manufacturing the first lens 3becomes difficult when the first lens 3 is manufactured by injectionmolding.

Therefore, by the value of d₂/d₁ being set to satisfy the expression(4), a means for effectively blocking unnecessary light can beappropriately employed while maintaining productivity.

The relationship between d₁ and d₂ is more preferably 0.65≦d₂/d₁≦1.1.

According to a more preferable embodiment, a condition expressed by afollowing expression (5) is further satisfied:0.65≦d ₂ /d ₃≦1.1  (5).where, d₃ in the expression (5) is a center thickness of the second lens4 (the same applies hereinafter).

Here, when the value of d₂/d₃ is less than the value (0.65) shown in theexpression (5), the distance between the first lens 3 and the secondlens 4 becomes too narrow. Inserting a blocking shield or the likebetween the first lens 3 and the second lens 4 to effectively blockunnecessary light becomes difficult. In addition, the edge sections ofrespective optical surfaces of the first lens 3 and the second lens 4become too close to each other, thereby increasing generation ofunnecessary light. On the other hand, when the value of d₂/d₃ is greaterthan the value (1.1) shown in the expression (5), the center thicknessof the second lens 4 becomes too thin. Manufacturing the second lens 4becomes difficult when the second lens 4 is manufactured by injectionmolding.

Therefore, by the value of d₂/d₃ being set to satisfy the expression(5), a means for effectively blocking unnecessary light can beappropriately employed while maintaining productivity.

The relationship between d₂ and d₃ is more preferably 0.65≦d₂/d₃≦1.

According to a more preferable embodiment, a condition expressed by afollowing expression (6) is further satisfied:0.1≦d ₁ /FL≦0.3  (6).

Here, when the value of d₁/FL is less than the value (0.1) shown in theexpression (6), the center thickness of the first lens 3 becomes toothin. Manufacturing the first lens 3 becomes difficult when the firstlens 3 is manufactured by injection molding. On the other hand, when thevalue of d₁/FL is greater than the value (0.3) shown in the expression(6), the center thickness of the first lens 3 becomes too thick comparedto the overall length of the optical system. Size and weight reductionbecomes difficult to achieve.

Therefore, by the value of d₁/FL being set to satisfy the expression(6), excellent balance can be further achieved between size and weightreduction and maintenance of productivity.

The relationship between d₁ and FL is more preferably 0.15≦d₁/FL≦0.3.

According to a more preferable embodiment, a condition expressed by afollowing expression (7) is further satisfied:0.1≦d ₃ /FL≦0.3  (7).

Here, when the value of d₃/FL is less than the value (0.1) shown in theexpression (7), the center thickness of the second lens 4 becomes toothin. Manufacturing the second lens 4 becomes difficult when the secondlens 4 is manufactured by injection molding. On the other hand, when thevalue of d₃/FL is greater than the value (0.3) shown in the expression(7), the center thickness of the second lens 4 becomes too thickcompared to the overall length of the optical system. Size and weightreduction becomes difficult to achieve.

Therefore, by the value of d₃/FL being set to satisfy the expression(7), productivity can be maintained while more effectively reducing sizeand weight.

The relationship between d₃ and FL is more preferably 0.15≦d₃/FL≦0.3.

According to a more preferable embodiment, a condition expressed by afollowing expression (8) is further satisfied:0.9≦L/FL≦1.2  (8)where, L in the expression (8) is an overall length of the lens systemor, in other words, a distance from the surface closest to the objectside to the image-taking surface 5 on the optical axis 6 (equivalent airlength) (the same applies hereinafter).

Here, when the value of L/FL is less than the value (0.9) shown in theexpression (8), the overall length of the optical system becomes tooshort. Productivity during an assembly process of each of the lenses 3and 4 deteriorates. On the other hand, when the value of L/FL is greaterthan the value (1.2) shown in the expression (8), the overall length ofthe optical system becomes too long. Mounting in a small camera of amobile phone or the like becomes difficult.

Therefore, by the value of L/FL being set to satisfy the expression (8),balance can be more effectively achieved between size and weightreduction and maintenance of productivity.

The relationship between L and FL is more preferably 1≦L/FL≦1.2.

A resin material of any composition can be used to form the first lens 3and the second lens 4 as long as the material has transparency and canbe used to form optical components, such as acrylic, polycarbonate, andamorphous polyolefin resin. To further improve production efficiency andfurther reduce manufacturing costs, the same resin material ispreferably used to form both lenses 3 and 4.

EXAMPLES

Next, EXAMPLES of the present invention will be described by referringto FIG. 2 to FIG. 27.

In the EXAMPLES, Fno denotes F number and r denotes the curvature radiusof the optical surface (the center radius curvature in the case of alens). Further, d denotes a distance to the next optical surface on theoptical axis 6, and denotes the index of refraction when the d line(yellow) is irradiated, and υd denotes the Abbe number of each opticalsystem also when the d line is irradiated.

k, A, B, C, and D denote each coefficient in a following expression (9).Specifically, the shape of the aspherical surface of the lens isexpressed by the following expression provided that the direction of theoptical axis 6 is taken as the Z axis, the direction orthogonal to theoptical axis 6 is taken as the X axis, the traveling direction of lightis positive, k is the constant of cone, A, B, C, and D are theaspherical coefficients, and r is the curvature radius.Z(X)=r− ¹ X ²/[1+{1−(k+1)r− ² X ²}^(1/2) ]+AX ⁴ +BX ⁶ +CX ⁸ +DX ¹⁰  (9)

In the following EXAMPLES, reference code E used for a numerical valuedenoting the constant of cone and the aspherical coefficient indicatesthat the numerical value following E is an exponent having 10 as thebase and that the numerical value before E is multiplied by thenumerical value denoted by the exponent having 10 as the base. Forexample, 7.93E+1 denotes 7.93×10¹.

First Example

FIG. 2 shows a FIRST EXAMPLE of the present invention. The lens 1 in theFIRST EXAMPLE is identical with the lens 1 whose composition is shown inFIG. 1. In the FIRST EXAMPLE, a surface apex (a point intersecting withan optical axis 6) and surrounding area of a first face 3 a of the firstlens 3 passes through the diaphragm 2 and is positioned closest to theobject side.

The imaging lens 1 of the FIRST EXAMPLE was set under the followingcondition.

Lens Data L = 1.67 mm, FL = 1.477 mm, f₁ = 1.444 mm, f₂ = −36.26 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.615 0.380 1.531 56.0 3(Second lens ofFirst lens) 2.400 0.260 4(First Face of Second Lens 4) −24.000 0.3901.531 56.0 5(Second Face of Second Lens) 100.000 (Imaging Surface) FaceNumber k A B C D 2 0 −1.88 7.93E+1 −2.22E+3 3.07E+4 3 0 −1.00 −1.17E+1−1.90E+2 4.46E+3 4 0 −7.55E−2 −1.63E+2 3.84E+3 −5.85E+4 5 0 −6.61E−1−2.62 −1.72E+1 2.00E+2

Under such conditions, r₁/r₂=0.256 was achieved, thereby satisfying theexpression (1). r₁/FL=0.416 was achieved, thereby satisfying theexpression (2). f₁/FL=0.978 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.26 was achieved, thereby satisfying theexpression (6). d₃/FL=0.26 was achieved, thereby satisfying theexpression (7). L/FL=1.131 was achieved, thereby satisfying theexpression (8).

FIG. 3 shows the astigmatism and distortion of the imaging lens 1 of theFIRST EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Second Example

FIG. 4 shows a SECOND EXAMPLE of the present invention. In the SECONDEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the SECOND EXAMPLE was set under the followingcondition.

Lens Data L = 1.69 mm, FL = 1.496 mm, f₁ = 1.467 mm, f₂ = −46.88 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.620 0.380 1.531 56.0 3(Second Face ofFirst Lens) 2.350 0.260 4(First Face of Second Lens) −25.000 0.390 1.53156.0 5(Second Face of Second Lens) 0.000 (Image Surface) Face Number k AB C D 2 0 −1.88 7.96E+1 −2.24E+3 3.09E+4 3 0 −1.08 −1.06E+1 −2.17E+24.66E+3 4 0 −9.78E−2 −1.60E+2 3.79E+3 −5.83E+4 5 0 −5.79E−1 −3.44−1.29E+1 1.86E+2

Under such conditions, r₁/r₂=0.264 was achieved, thereby satisfying theexpression (1). r₁/FL=0.414 was achieved, thereby satisfying theexpression (2). f₁/FL=0.981 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.25 was achieved, thereby satisfying theexpression (6). d₃/FL=0.26 was achieved, thereby satisfying theexpression (7). L/FL=1.130 was achieved, thereby satisfying theexpression (8).

FIG. 5 shows the astigmatism and distortion of the imaging lens 1 of theSECOND EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Third Example

FIG. 6 shows a THIRD EXAMPLE of the present invention. In the THIRDEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the THIRD EXAMPLE was set under the followingcondition.

Lens Data L = 1.68 mm, FL = 1.49 mm, f₁ = 1.466 mm, f₂ = −59.42 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.6195 0.380 1.531 56.0 3(Second Face ofFirst Lens) 2.3467 0.260 4(First Face of Second Lens) −25.8700 0.3901.531 56.0 5(Second Face of Second Lens) −141.6000 (Image Surface) FaceNumber k A B C D 2 0 −1.81 7.89E+1 −2.23E+3 3.09E+4 3 0 −1.27 −1.69−3.40E+2 5.29E+3 4 0 −8.35E−1 −1.37E+2 3.49E+3 −5.66E+4 5 0 −8.29E−1−9.67E−1 −1.86E+1 1.55E+2

Under such conditions, r₁/r₂=0.264 was achieved, thereby satisfying theexpression (1). r₁/FL=0.416 was achieved, thereby satisfying theexpression (2). f₁/FL=0.984 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.26 was achieved, thereby satisfying theexpression (6). d₃/FL=0.26 was achieved, thereby satisfying theexpression (7). L/FL=1.128 was achieved, thereby satisfying theexpression (8).

FIG. 7 shows the astigmatism and distortion of the imaging lens 1 of theTHIRD EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Fourth Example

FIG. 8 shows a FOURTH EXAMPLE of the present invention. In the FOURTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the FOURTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.74 mm, FL = 1.561 mm, f₁ = 1.52 mm, f₂ = −34.41 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.630 0.370 1.531 56.0 3(Second Face ofFirst Lens) 2.250 0.260 4(First Face of Second Lens) −22.500 0.380 1.53156.0 5(Second Face of Second Lens) 100.000 (Image Surface) Face Number kA B C D 2 0 −1.85 7.74E+1 −2.20E+3 2.98E+4 3 0 −1.48 −7.51 −2.93E+25.17E+3 4 0 −6.43E−1 −1.52E+2 3.70E+3 −5.84E+4 5 0 −6.02E−1 −4.34 −8.841.89E+2

Under such conditions, r₁/r₂=0.280 was achieved, thereby satisfying theexpression (1). r₁/FL=0.404 was achieved, thereby satisfying theexpression (2). f₁/FL=0.974 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.70 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.68 was achieved, thereby satisfying theexpression (5). d₁/FL=0.24 was achieved, thereby satisfying theexpression (6). d₃/FL=0.24 was achieved, thereby satisfying theexpression (7). L/FL=1.115 was achieved, thereby, satisfying theexpression (8).

FIG. 9 shows the astigmatism and distortion of the imaging lens 1 of theFOURTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Fifth Example

FIG. 10 shows a FIFTH EXAMPLE of the present invention. In the FIFTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the FIFTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.72 mm, FL = 1.542 mm, f₁ = 1.51 mm, f₂ = −46.88 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.625 0.380 1.531 56.0 3(Second Face ofFirst Lens) 2.200 0.240 4(First Face of Second Lens) −25.000 0.370 1.53156.0 5(Second Face of Second Lens) 0.000 (Image Surface) Face Number k AB C D 2 0 −1.91 7.92E+1 −2.24E+3 3.06E+4 3 0 −1.54 −1.07E+1 −2.74E+25.03E+3 4 0 −5.41E−1 −1.69E+2 4.03E+3 −6.11E+4 5 0 −6.29E−1 −5.21−2.94E−1 1.67E+2

Under such conditions, r₁/r₂=0.284 was achieved, thereby satisfying theexpression (1). r₁/FL=0.405 was achieved, thereby satisfying theexpression (2). f₁/FL=0.979 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.63 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.65 was achieved, thereby satisfying theexpression (5). d₁/FL=0.25 was achieved, thereby satisfying theexpression (6). d₃/FL=0.24 was achieved, thereby satisfying theexpression (7). L/FL=1.115 was achieved, thereby satisfying theexpression (8).

FIG. 11 shows the astigmatism and distortion of the imaging lens 1 ofthe FIFTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Sixth Example

FIG. 12 shows a SIXTH EXAMPLE of the present invention. In the SIXTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the SIXTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.73 mm, FL = 1.541 mm, f₁ = 1.515 mm, f₂ = −62.62 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.625 0.380 1.531 56.0 3(Second Face ofFirst Lens) 2.175 0.260 4(First Face of Second Lens) −25.000 0.390 1.53156.0 5(Second Face of Second Lens) −100.000 (Image Surface) Face Numberk A B C D 2 0 −1.82 7.83E+1 −2.21E+3 3.00E+4 3 0 −1.25 −7.28 −2.75E+25.02E+3 4 0 −4.85E−1 −1.46E+2 3.58E+3 −5.73E+4 5 0 −6.14E−1 −2.56−2.13E+1 2.22E+2

Under such conditions, r₁/r₂=0.287 was achieved, thereby satisfying theexpression (1). r₁/FL=0.406 was achieved, thereby satisfying theexpression (2). f₁/FL=0.983 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.25 was achieved, thereby satisfying theexpression (6). d₃/FL=0.25 was achieved, thereby satisfying theexpression (7). L/FL1.123 was achieved, thereby satisfying theexpression (8).

FIG. 13 shows the astigmatism and distortion of the imaging lens 1 ofthe SIXTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Seventh Example

FIG. 14 shows a SEVENTH EXAMPLE of the present invention. In the SEVENTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the SEVENTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.74 mm, FL = 1.557 mm, f₁ = 1.531 mm, f₂ = −62.62 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.625 0.380 1.531 56.0 3(Second Face ofFirst Lens) 2.100 0.260 4(First Face of Second Lens) −25.000 0.390 1.53156.0 5(Second Face of Second Lens) −100.000 (Image Surface) Face Numberk A B C D 2 0 −1.78 7.65E+1 −2.14E+3 2.89E+4 3 0 −1.35 −1.54 −3.57E+25.49E+3 4 0 −1.02 −1.25E+2 3.26E+3 −5.54E+4 5 0 −7.43E−1 −2.87 1.853.79E+1

Under such conditions, r₁/r₂=0.298 was achieved, thereby satisfying theexpression (1). r₁/FL=0.401 was achieved, thereby satisfying theexpression (2). f₁/FL=0.983 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.24 was achieved, thereby satisfying theexpression (6). d₃/FL=0.25 was achieved, thereby satisfying theexpression (7). L/FL=1.118 was achieved, thereby satisfying theexpression (8).

FIG. 15 shows the astigmatism and distortion of the imaging lens 1 ofthe SEVENTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Eighth Example

FIG. 16 shows a EIGHTH EXAMPLE of the present invention. In the EIGHTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the EIGHTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.34 mm, FL = 1.206 mm, f₁ = 1.18 mm, f₂ = −32.12 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0302(First Face of First Lens) 0.480 0.290 1.531 56.0 3(Second Face ofFirst Lens) 1.600 0.200 4(First Face of Second Lens) −20.000 0.300 1.53156.0 5(Second Face of Second Lens) 120.000 (Image Surface) Face Number kA B C D 2 0 −3.95 2.91E+2 −1.38E+4 3.19E+5 3 0 −3.01 −5.84 −2.31E+36.06E+4 4 0 −2.27 −4.74E+2 2.11E+4 −6.11E+5 5 0 −1.65 −1.09E+1 1.20E+14.19E+2

Under such conditions, r₁/r₂=0.300 was achieved, thereby satisfying theexpression (1). r₁/FL=0.398 was achieved, thereby satisfying theexpression (2). f₁/FL=0.978 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.69 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.24 was achieved, thereby satisfying theexpression (6). d₃/FL=0.25 was achieved, thereby satisfying theexpression (7). L/FL=1.111 was achieved, thereby satisfying theexpression (8).

FIG. 17 shows the astigmatism and distortion of the imaging lens 1 ofthe EIGHTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Ninth Example

FIG. 18 shows a NINTH EXAMPLE of the present invention. In the NINTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the NINTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.80 mm, FL = 1.633 mm, f₁ = 1.604 mm, f₂ = −62.62 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.6329 0.380 1.531 56.0 3(Second Face ofFirst Lens) 1.9231 0.260 4(First Face of Second Lens) −25.0000 0.3901.531 56.0 5(Second Face of Second Lens) −100.0000 (Image Surface) FaceNumber k A B C D 2 0 −1.54 6.11E+1 −1.70E+3 2.31E+4 3 0 −1.34 −5.72−2.41E+2 4.03E+3 4 0 −1.41 −1.07E+2 2.97E+3 −5.37E+4 5 0 −1.03 2.49−4.80E+1 2.92E+2

Under such conditions, r₁/r₂=0.329 was achieved, thereby satisfying theexpression (1). r₁/FL=0.388 was achieved, thereby satisfying theexpression (2). f₁/FL=0.982 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.23 was achieved, thereby satisfying theexpression (6). d₃/FL=0.24 was achieved, thereby satisfying theexpression (7). L/FL=1.102 was achieved, thereby satisfying theexpression (8).

FIG. 19 shows the astigmatism and distortion of the imaging lens 1 ofthe NINTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Tenth Example

FIG. 20 shows a TENTH EXAMPLE of the present invention. In the TENTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the TENTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.33 mm, FL = 1.213 mm, f₁ = 1.183 mm, f₂ = −28.58 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0302(First Face of First Lens) 0.465 0.280 1.531 56.0 3(Second Face ofFirst Lens) 1.400 0.190 4(First Face of Second Lens) −18.000 0.285 1.53156.0 5(Second Face of Second Lens) 100.000 (Image Surface) Face Number kA B C D 2 0 −3.89 2.85E+2 −1.47E+4 3.71E+5 3 0 −3.38 −2.67E+1 −2.08E+36.46E+4 4 0 −3.56 −4.99E+2 2.57E+4 −8.60E+5 5 0 −2.59 1.16E+1 −4.15E+24.67E+3

Under such conditions, r₁/r₂=0.332 was achieved, thereby satisfying theexpression (1). r₁/FL=0.383 was achieved, thereby satisfying theexpression (2). f₁/FL=0.975 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.23 was achieved, thereby satisfying theexpression (6). d₃/FL=0.23 was achieved, thereby satisfying theexpression (7). L/FL=1.096 was achieved, thereby satisfying theexpression (8).

FIG. 21 shows the astigmatism and distortion of the imaging lens 1 ofthe TENTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Eleventh Example

FIG. 22 shows a ELEVENTH EXAMPLE of the present invention. In theELEVENTH EXAMPLE, a surface apex a surface apex (a point intersectingwith an optical axis 6) and surrounding area of a first face 3 a of thefirst lens 3 passes through the diaphragm 2 and is positioned closest tothe object side.

The imaging lens 1 of the ELEVENTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.38 mm, FL = 1.266 mm, f₁ = 1.237 mm, f₂ = −33.75 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0302(First Face of First Lens) 0.475 0.280 1.531 56.0 3(Second Face ofFirst Lens) 1.350 0.190 4(First Face of Second Lens) −18.000 0.280 1.53156.0 5(Second Face of Second Lens) 0.000 (Image Surface) Face Number k AB C D 2 0 −3.56 2.56E+2 −1.33E+4 3.38E+5 3 0 −4.09 1.14E+1 −3.17E+37.59E+4 4 0 −4.57 −4.49E+2 2.44E+4 −8.48E+5 5 0 −2.62 1.34E+1 −4.52E+24.88E+3

Under such conditions, r₁/r₂=0.352 was achieved, thereby satisfying theexpression (1). r₁/FL=0.375 was achieved, thereby satisfying theexpression (2). f₁/FL=0.977 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.68 was achieved, thereby satisfying theexpression (5). d₁/FL=0.22 was achieved, thereby satisfying theexpression (6). d₃/FL=0.22 was achieved, thereby satisfying theexpression (7). L/FL=1.090 was achieved, thereby satisfying theexpression (8).

FIG. 23 shows the astigmatism and distortion of the imaging lens 1 ofthe ELEVENTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Twelfth Example

FIG. 24 shows a TWELFTH EXAMPLE of the present invention. In the TWELFTHEXAMPLE, a surface apex (a point intersecting with an optical axis 6)and surrounding area of a first face 3 a of the first lens 3 passesthrough the diaphragm 2 and is positioned closest to the object side.

The imaging lens 1 of the TWELFTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.89 mm, FL = 1.734 mm, f₁ = 1.721 mm, f₂ = −188 mm, Fno =2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.040 2(FirstFace of First Lens) 0.645 0.380 1.531 56.0 3(Second Face of First Lens)1.725 0.260 4(First Face of Second Lens) −50.000 0.390 1.531 56.05(Second Face of Second Lens) −100.000 (Image Surface) Face Number k A BC D 2 0 −8.42E−1 1.51E+1 −2.70E+2 9.20E+2 3 0 −1.25 −2.38E+1 3.66E+2−5.27E+3 4 0 −2.42 −7.03E+1 2.42E+3 −5.07E+4 5 0 −1.12 2.09 −2.38E+15.27E+1

Under such conditions, r₁/r₂=0.374 was achieved, thereby satisfying theexpression (1). r₁/FL=0.372 was achieved, thereby satisfying theexpression (2). f₁/FL=0.993 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.22 was achieved, thereby satisfying theexpression (6). d₃/FL=0.22 was achieved, thereby satisfying theexpression (7). L/FL=1.090 was achieved, thereby satisfying theexpression (8).

FIG. 25 shows the astigmatism and distortion of the imaging lens 1 ofthe TWELFTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

Thirteenth Example

FIG. 26 shows a THIRTEENTH EXAMPLE of the present invention. In theTHIRTEENTH EXAMPLE, a surface apex (a point intersecting with an opticalaxis 6) and surrounding area of a first face 3 a of the first lens 3passes through the diaphragm 2 and is positioned closest to the objectside.

The imaging lens 1 of the THIRTEENTH EXAMPLE was set under the followingcondition.

Lens Data L = 1.95 mm, FL = 1.816 mm, f₁ = 1.776 mm, f₂ = −48.82 mm, Fno= 2.8 Face Number r d n d ν d (Object Point) 1(Diaphragm) ∞ −0.0402(First Face of First Lens) 0.650 0.380 1.531 56.0 3(Second Face ofFirst Lens) 1.650 0.260 4(First Face of Second Lens) −50.000 0.390 1.53156.0 5(Second Face of Second Lens) 50.000 (Image Surface) Face Number kA B C D 2 0 −5.42E−1 3.24E−1 4.46E+1 −2.33E+3 3 0 −1.53 −2.29E+1 3.56E+2−4.94E+3 4 0 −3.19 −5.34E+1 2.15E+3 −4.93E+4 5 0 −1.01 −2.28 2.64E+1−2.73E+2

Under such conditions, r₁/r₂=0.394 was achieved, thereby satisfying theexpression (1). r₁/FL=0.358 was achieved, thereby satisfying theexpression (2). f₁/FL=0.978 was achieved, thereby satisfying theexpression (3). d₂/d₁=0.68 was achieved, thereby satisfying theexpression (4). d₂/d₃=0.67 was achieved, thereby satisfying theexpression (5). d₁/FL=0.21 was achieved, thereby satisfying theexpression (6). d₃/FL=0.21 was achieved, thereby satisfying theexpression (7). L/FL=1.074 was achieved, thereby satisfying theexpression (8).

FIG. 27 shows the astigmatism and distortion of the imaging lens 1 ofthe THIRTEENTH EXAMPLE.

According to the result, each of the astigmatism and distortion wasalmost satisfied. It can be seen from the result that a sufficientoptical property can be obtained.

The present invention is not limited to the above-described embodimentsand EXAMPLES, and various modifications are possible as required.

1. An imaging lens used for forming an image of an object on animage-taking surface of an image sensor element, including: in orderfrom an object side to an image surface side, a diaphragm, a first lensthat is a meniscus lens having a positive power whose convex surfacefaces the object side, and a second lens that is a lens having anegative power whose concave surface faces the object side, whereinconditions expressed by the following expressions (1) to (3) are to besatisfied:0.25<r ₁ /r ₂≦0.45  (1)0.35≦r ₁ /FL≦0.42  (2)0.85≦f ₁ /FL≦1  (3) where, r₁: center radius curvature of the objectside face of the first lens r₂: center radius curvature of the imagesurface side face of the first lens FL: focal distance of the entirelens system f₁: focal distance of the first lens.
 2. The imaging lensaccording to claim 1, wherein, further, a condition expressed by afollowing expression (4) is to be satisfied:0.6≦d ₂ /d ₁≦1.25  (4) where, d₁: center thickness of the first lens d₂:distance between the first lens and the second lens on the optical axis.3. The imaging lens according to claim 1, wherein, further, a conditionexpressed by a following expression (5) is to be satisfied:0.65≦d ₂ /d ₃≦1.1  (5) where, d₂: distance between the first lens andthe second lens on the optical axis d₃: center thickness of the secondlens.
 4. The imaging lens according to claim 1, wherein, further, acondition expressed by a following expression (6) is to be satisfied:0.1≦d ₁ /FL≦0.3  (6) where, d₁: center thickness of the first lens. 5.The imaging lens according to claim 1, wherein, further, a conditionexpressed by a following expression (7) is to be satisfied:0.1≦d ₃ /FL≦0.3  (7) where, d₃: center thickness of the second lens. 6.The imaging lens according to claim 1, wherein, further, a conditionexpressed by a following expression (8) is to be satisfied:0.9≦L/FL≦1.2  (8) where, L: overall length of the lens system (distancefrom the surface closest to the object side to the image-taking surfaceon the optical axis: equivalent air length).